Industrial robot wrist unit

ABSTRACT

A wrist unit for an industrial robot comprises a wrist housing detachably mounted to a distal end of a robot arm, the wrist housing containing rotatably mounted first and second, parallel, secondary drive shafts on the input ends of which are mounted cylindrical driven gears for engagement with the respective cylindrical drive gears located on primary drive shafts on the robot arm. The driven gears and the drive gears are so disposed that an imaginary line extending through the centers of the gears are offset from the center axis of the coaxial drive gears, the wrist housing being radially adjustable on the end of the robot arm for adjusting the gear clearance between the drive gears and the driven gears.

BACKGROUND OF THE INVENTION

The present invention relates to an industrial robot wrist unit,comprising a wrist housing, which is intended to be detachably fixed toa distal end of a robot arm and in which there is pivotally mounted atilt housing, which in turn supports a rotatably mounted turntable onwhich there can be mounted an external tool, first and second secondarydrive shafts being rotatably mounted in the wrist housing, the first andsecond secondary drive shafts each having an input end which supports agear for engagement with a respective drive gear on a respective primarydrive shaft in the robot arm, the drive gears being disposed coaxial toeach other and axially spaced, and where the first secondary drive shaftvia a respective first gearing can rotate the turntable about a firstaxis and the second secondary drive shaft can, via a respective secondgearing, pivot the tilt housing about a second axis, which crosses thefirst axis.

In a previously known wrist unit of the above mentioned type, the wristhousing comprises two halves, where each half has a through-hole for arespective secondary drive shaft. When assembled, the center axes of theholes for the secondary drive shafts in the housing halves, and therebythe center axis of the gears thereon, are disposed on diametricallyopposite sides of the central coaxial driving gears on the primary driveshafts in the robot arm with which they are in engagement. In otherwords a straight line extends through the center axes of the secondarygears and the coaxial drive gears. This has made it difficult to adjustthe clearance between the drive gears and their respective gears on thesecondary drive shafts.

SUMMARY OF THE INVENTION

A primary purpose of the present invention is to suggest a wrist unit inwhich the aforementioned gear clearance can be easily adjusted. This isachieved by a wrist unit of the general type in which the gears and thedrive gears (as seen in an end view projection) are placed relative toeach other so that an imaginary line, extending through the centers ofthe gears, is offset from the centerline through the gears and that thewrist housing is radially adjustably fixable on the end of the robot armfor adjusting the gear clearance between, on the one hand, the drivegears on the primary drive shafts and, on the other hand, the gears onthe secondary drive shafts.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in more detail below with reference tothe accompanying drawing, in which:

FIG. 1 is a partially sectioned longitudinal view of a wrist unit inaccordance with the invention, mounted on a distal end of a robot arm;and

FIG. 2 is an end view of the wrist unit shown in FIG. 1 as seen from theend of the robot arm.

DETAILED DESCRIPTION OF THE INVENTION

With reference to FIG. 1, there is shown a wrist generally designated10, for an industrial robot in accordance with the invention. The wrist10 comprises in principle, a distal, fork-shaped wrist housing 12 withtwo fork arms 14 and 16, defining between them a groove-shaped space,the side walls 18,20 and bottom wall 22 of which are indicated in FIG.1.

The wrist housing 12 is intended to be mounted on the distal end of arobot arm 24 by means of screw fasteners (not shown). FIG. 2 shows,however, four through-holes 26 for the anchoring screws in an anchoringflange 28 of the housing 12.

In the wrist housing 12 there is a so-called tilt housing 30 pivotallymounted about a transverse axis A and which supports in a manner knownper se a turntable 32, which is rotatably mounted about a longitudinallyoriented axis B. On the turntable 32 there can be mounted a chosen tool(not shown), such as a welding unit, gripping means, a spray-paintingnozzle or the like. The portion of the tilt housing 30 supporting theturntable 32 and its shaft 34 is thus pivotable about the axis A in thespace between the fork arms 14,16 through an arc of less than 360°. Theaxis A is oriented perpendicular to the rotational axis B of theturntable 32.

For rotation of the turntable 32, there is mounted in the wrist housing12 a first secondary drive shaft 36 which extends through a hole in thelongitudinal direction of the housing 12, preferably parallel to therotational axis B of the turntable 32. The drive shaft 36, which can beaxially and radially mounted in a double-row angular contactball-bearing 38, has an input end 40 on which there is non-rotatablymounted a preferably cylindrical gear 42 which engages a preferablycylindrical driving gear 44 on the end of a first primary drive shaft 46which is insertable into the wrist housing 12 of the robot arm 24. Theother end of the secondary drive shaft 36 is an output end which is inthe form of a hypoid pinion 48, which engages a hypoid gear 50, which isrotatably mounted about the axis A perpendicular to the drive shaft 36and on the outside of the pinion 48. The hypoid pinion 48 and the hypoidgear 50 thus form together a first hypoid gearing. In the hub of thehypoid gear 50 there is non-rotatably mounted a conical drive gear 52,which in turn engages a bevel gear 54 rotatably mounted in the tilthousing 30 and non-rotatably joined to the shaft 34 of the turntable 32.

When the first primary drive shaft 46 in the robot arm 24 is rotated,the rotary movement is thus transmitted via the gearing 44,42 to thesecondary drive shaft 36, which in turn, via the first hypoid gearing48,50 and the angle gearing 52,54 imparts a rotary movement about theaxis B to the shaft 34 and thus the turntable 32. The axis B in theneutral position shown in FIG. 1 is coaxial with the center axis C ofthe primary drive shaft 46. The center axis C is preferably also an axisabout which the robot arm 24 itself can rotate.

For pivoting the tilt housing 30 about the axis A in the wrist housing12, a second secondary drive shaft 56 is also rotatably mounted therein.The secondary drive shaft 56 extends through a hole in the longitudinaldirection of the housing 12, preferably parallel to the first secondarydrive shaft 36. As is the first secondary drive shaft 36, the secondsecondary drive shaft 56 is axially and radially mounted in a two-rowangular contact ball bearing 58 and has an input end 60 on which thereis non-rotatably mounted a preferably cylindrical gear 62, which engagesa preferably cylindrical drive gear 64 on the end of a second primarydrive shaft 66 in the robot arm 24. The drive gear 64 is disposedcoaxial to, but axially spaced from the cylindrical drive gear 44 on thefirst primary drive shaft 46. In the embodiment shown in the drawing,the cylindrical drive gears 44,64 and the gears 42,62 have an equalnumber of teeth, and therefore the gear ratio between the respectiveprimary and secondary drive shafts 46,36 and 66,56 is 1:1. The number ofteeth and therefore the gear ratio in these gearings can of course bevaried as desired.

The other end of the second secondary drive shaft 56 is an output end,which, as is the first secondary drive shaft 36, is in the form of ahypoid pinion 68, which engages a hypoid gear 70 which is rotatablymounted about the axis A perpendicular to the secondary drive shaft 56and coaxial to the hypoid gear 50 in the first hypoid gearing 48,50. Thehypoid gear 50 is located outside the pinion 68. The hypoid gear 70 issecurely joined by screws 72 to the tilt housing 30.

As the second primary drive shaft 66, which coaxially encloses the firstprimary drive shaft 46 in the robot arm 24, rotates, the rotary movementis thus transmitted via the cylindrical gearing 64,62 to the secondsecondary drive shaft 56, which in turn transmits, via the second hypoidgearing 68,70, the rotation to the tilt housing 30 and the turntable 32mounted therein about the axis A.

In accordance with a preferred embodiment of the wrist housing 12 of theinvention, the center axes D and E of the secondary drive shafts 36,56and thus their cylindrical gears 42,62 are located (as can be seen inFIG. 2) on the same side of a central midplane F through the coaxialcylindrical drive gears 44,64, so that an imaginary line L, extendingthrough the centers D,E of the gears 42,62, will be spaced from thecenter C of the coaxial drive gears 44,64. This means that it will bepossible to adjust at the same time the gear engagement and thus theclearance between the two cylindrical gear trains 44,42 and 64,62,respectively, by means of a small radial displacement of the entirewrist housing 12 in the direction of the arrow P in FIG. 2. This isachieved by loosening a screw fastener (not shown) between the housing12 and the arm 24 and placing an adjustment tool (not shown) against thehousing 12 to adjust the gear clearance in the gearings to a desiredvalue, preferably with minimum clearance, by radial adjustment of thehousing through the holes 26.

The housing 12 is in a preferred embodiment of the invention made in onepiece, thus achieving a number of advantages over conventionally dividedhousings. There will thus be no problems with fitting the halves of thehousing when assembling the wrist. It is also simpler to achieve highmanufacturing tolerances when machining holes and abutment surfaces inthe housing when it is made as one piece. The assembly of gearing,bearings, seals and the like is also facilitated. No screws holding thehousing halves together are required, which would otherwise give rise toundesirable movement between the housing halves. Finally, a fewer numberof seals are required to prevent dirt from penetrating into the wristand preventing any oil in the wrist gearings from leaking out from thehousing.

What is claimed is:
 1. A wrist unit for an industrial robot, comprisinga wrist housing detachably mounted to a distal end of a robot arm, thewrist housing including a pivotally mounted tilt housing which supportsa rotatably mounted turntable for supporting an external tool, first andsecond secondary drive shafts rotatably mounted in the wrist housing,said first and second secondary drive shaft each having an input endsupporting driven gears for engagement with drive gears respectivelylocated on primary drive shafts in the robot arm, said drive gears beingcoaxial and axially spaced, the turntable being rotatable about a firstaxis by the first secondary drive shaft via a respective first gearing,the tilt housing being pivotable about a second axis by the secondsecondary drive shaft via a respective second gearing, and the first andsecond axes intersecting, the improvement wherein the driven gears andthe drive gears are disposed relative to each other so that an imaginaryline, extending through centers of the driven gears, is offset from acenterline of the drive gears, and wherein the wrist housing is radiallyadjustable on the end of the robot arm for adjusting the gear clearancebetween the drive gears and the driven gears.
 2. The wrist unitaccording to claim 1 wherein the driven gears and the drive gears areeach cylindrical.
 3. The wrist unit according to claim 1 wherein thewrist housing is of a single piece construction.